Despite the excitement and investment, it is far from clear how much of the activity on these sites involves productive engagement, and how much is just passing curiosity -- or a desire to access papers shared by other users that they might otherwise have to pay for.

Some irritated scientists say that the site taps into human instincts only too well -- by regularly sending out automated e-mails that profess to come from colleagues active on the site, thus luring others to join on false pretences. (Indeed, 35% of regular ResearchGate users in Nature's survey said that they joined the site because they received an e-mail.)

... where and when they are downloaded. "I find it especially intriguing that my most downloaded paper is not my most cited work," she says. "To put it bluntly, I have no idea if these sites have any impact whatsoever on my career -- I tend to doubt they do -- but I enjoy knowing that my work is being discussed."

La preocupación de las editoriales por las descargas 'ilegales':

Publishers are worried that the sites could become public troves of illegally uploaded content. In late 2013, Elsevier sent 3,000 notices to ...

Y la forma que van teniendo, por ahora, de ganar dinero:

Madisch says that ResearchGate will not sell its user data, and that it already makes some money by running job adverts (as does Academia.edu). In the future, he hopes to add a marketplace for laboratory services and products, connecting companies and corporate researchers to academics (28% of the network's users are from the corporate world, he says).